Experimental Investigation of Fe–Co–La System: Liquidus and Solidus Projections

Abstract

Phase equilibria in the Co-Fe-La system were studied using differential thermal analysis (DTA), X-ray diffraction analysis, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Liquidus and solidus projections and a melting diagram for this system over the whole concentration range and a Scheil diagram for solidification were constructed. The ternary compound (Co,Fe) 17 La 2 (s) (Th 2 Zn 17 -type structure) forms by peritectic reaction L ? (cCo,Fe) ? Co 13 La ¢ s at 978°C. This ternary compound is located along the isoconcentrate of 11 at.% La and extends from 45.8 to 79.3 at.% Co. The Co 13 La phase has the widest homogeneity region and dissolves up to 43.3 at.% Fe. The solubilities of Fe in Co 5 La, Co 7 La 2 , Co 19 La 5 , and Co 3 La 2 were established to be 10.3, 9.2, 4.7, and 3.2 at.%, respectively. The solubility of Fe in Co 1.7 La 2 and CoLa 3 according to EPMA does not exceed 1 at.%. The maximum solubility of La in (cCo,Fe) and (aCo,Fe) is determined to be less than 1 at.%.

Experimental Investigation of Isothermal Section in the La–Co–Ni System at 723 K

“…By optimizing the Fe/Co/Ni/Si ratio of the La(FeCoNiSi) 13 alloy, the magnetic phase transition temperature of the alloy can be adjusted to room temperature, which makes the application of magnetic refrigeration technology at room temperature very possible. Phase diagrams are very important for studying the effects of the elements and are beneficial for alloys in design and fabrication [11][12][13][14][15]. Up to now, however, the current report on the isothermal section of the La-Co-Ni ternary system is the La < 32.2% isothermal section of the La-Co-Ni ternary phase diagram determined by Zheng et al [16] in 1981, and the phase diagram of La-Co-Ni is not complete.…”